Digester strainer



Sept. 16, 1958 P. EYoLFsoN 2,852,369

DIGESTER STRAINER Filed Sept. 17. 1954 3 Sheets-Sheet 1 FIG. 2

INVEN T0124., PAUL EYOL FSON www A T TORNE VI sept. 16, 195s P, EYOLFSON 2,852,369

DIGESTER STRAINER INVENTOIL' PAUL EYoLFsoN MMM Sept. 16, 1958 P. r-:YoLFsoN 2,852,369

DIGESTER STRAINER Fird sept. 17. 1954 s sheets-sheet s IN VEN TOR. PAUL EYOLFSON BWM. Mw

ATTORNEYS United States Patent O 2,852,369 DIGESTER STRAINER Paul Eyolfson, Portland, Oreg., assignor to Electric Steel Foundry, Portland, Greg., a corporation of Oregon Application September 17, 1954, Serial No. 456,754

8 Claims. (Cl. 92-7) The present invention relates to digester screens, particularly digester screens used in the pulp and paper industries. Digesters are normally employed as pressure cooking vessels for wood chips and related cellulosic materials which are to be subjected to the action of a hot liquid capable of breaking down the mechanical structure of the materials so that the fibers thereof are rendered available for subsequent treatment into pulp, paper and related substances. Digesters are usually coupled with a circulating system by means of which the cooking liquor is kept in circulation and its temperature and strength controlled. The liquor is drawn from the digester through a suction pipe leading to la circulating pump, and is returned to the digester after treatment. Digester screens are provided inside of the digester vessel to prevent the escape of chips and other large material which would clog the pump or other parts of the circulating system. In accordance with 'best design, the digester screen is composed of a plurality of separable sections defining a hollow annulus encircling the interior wall of the digester at an intermediate point, the interior of the annulus communicating with the suction pipe of the circulating system. The present invention comprises an improvement inl sectional digester screens, whereby extreme economies in manufacturing, mounting, and maintenance of the digester screens are effected.

A principal object of the present invention is to provide a digester screen section comprising a frame which may be cast as a unitary, complete frame suitable for use in all commercially used sizes of digesters, ranging from approximately eight feet to approximately eighteen feet in diameter. Advantages of the achievement of this object of the invention are numerous. For example, the foundary requires only one digester screen frame mold, rather than a large number each designed for a single diameter of digester; the foundary may keep a stock of digester screen frames on hand Iand have them readily available to fill any order, rather than make custom ones to ll particular orders; the pulp and paper mills may keep a stock of replacement frames on hand, rather than a far larger stock of replacement frames designed for various diameters of digesters; and pulp and paper mills may salvage digester frames in the event that they enlarge `or decrease the diameters of their digesters.

A further object of the present invention is to provide a digester screen `section which may be easily mounted in the digester by ordinary workmen, there being no special ttings required, and the spacing between adjoining sections of the digester screen not being critical.

A further object of the present invention is to provide a digester screen section comprising a frame and screening means mounted thereon, in which a plurality of rectangular, at, perforated sheets are utilized to provide the screening means, thereby simplifying the fabrication of the digester screen section.

A further object of the present invention is to provide a digester screen section permitting the rapid placement and temporary tacking in place of flat screen plates, and which screen plates may 'be easily removed for replacement in the event of extreme corrosion thereof, whereby the cast frames may be salvaged.

The foregoing and other yobjects and advantages of the present invention will be more readily apparent from inspection of the accompanying drawing taken in connection with the following specification wherein like numerals refer to like parts throughout.

In the drawing:

Fig. l is `a partial elevation of a digester with parts broken away to illustrate the digester screen;

Fig. 2 is an enlargement of a portion of Fig. 1 illustrating the present invention;

Fig. 3 is an enlarged, outer surface View of one of the digester sections, ltogether with the overlapped edge 'of an adjacent digester section in the relationship they might occupy when in use;

Fig. 4 is a partially broken away side view of one digester section;

Fig. 5 is a bottom view of one digester section;

Fig. 6 is a horizontal central section through part of a digester screen lbuilt in accordance with the present invention in use in a maximum diameter dig-ester;

Fig. 7 is a view similar to Fig. 6, showing the present invention in use in a minimum diameter digester; and

Fig. 8 is a view in perspective of the outer surfaces of portions of a pair of the digester frames in use.

In the drawings, a digester comprising a cylindrical steel shell 10 and an inner-refractory lining 11 is illustrated, the digester having a digester screen 12 mounted therein, the latter comprising aplurality Vof digester sections 13. The digester sections are clamped in position at top and bottom by a plurality of Z-strip support ring segments 14 having elongated, horizontal lslots 15 for reception of mounting bolts 16 suitably secured to the steel shell 10 and extending through the ceramic liner 11. Each of the sections comprises a frame including an upper, horizontal bearing segment 17, a lower, horizontal bearing segment 18, and a plurality of vertical, arched ribs extending therebetween, preferably there being a pair of side ribs 19 and 20 and a pair of intermediate ribs 21. The structure is preferably braced by an upper crossbar 22 and a lower crossbar 23. The crossbars and side ribs frame a vertically disposed, central screen plate 24 which extends laterally from rib 19 to rib 20. The upper brace 22 and the upper bearing segment 17, together with the side ribs 19 and 20, frame an upper screen plate 25. The lower brace 23 and the lower bearing segment 18, together with the side ribs 19 and 2t), frame a lower screen plate 26. T-he inner surfaces of the intermediate ribs 21 are lower than the outer surfaces of the side ribs 19 and 20 so that-the at screen plates are retained in a framing depression.

Similarly, the braces 22 and 23 are raised above the intermediate ribs 21, `and ns 27 and 28 formed respectively on the upper and lower bearing segments l17 and 18 also provide elevated frame members for the adjacent edges of the rectangular screen plates. The screen plates form llush surfaces with the exposed inner surfaces of the intermediate ribs 21, the side rib 20, the

crossbars 22 and23, and the fins 27 and 28, thestructurel as a whole being free from ledges or other protrusions which would cause the chips or other material to lodge thereon. f

One vertical edge of each frame is provided with a laterally extending flange 29 from end to end thereof,

which llange is raised above the adjacent surfaces of the frame so that its outwardly facing surface may overlie.

and engage the inner surface jof the .opposite edge of an adjoining frame. As seen most clearly in Fig. 4, the ange 29, which is herein termed a covering ange, merges into the inner surfaces of the bearing segments at both of its ends, the bearing segments being extended beyond the side rib 19. The other side rib supports a continuous flange extending from end to end thereof, but the opposite ends of which merge into the inner surface of the bearing segments, and the inner surface of which lies flush with the major planes of the screen plates. Each of the flanges 29 and 3l) is progressively decreased in width from its ends toward the middle, the ange 30 considerably more so than the ange 29. Since both flanges are so shaped, the sum of the widths thereof progressively decreases from their ends toward their middles. The ange 3@ is herein referred to as the covered flange, for convenience of reference. The ends of the flange 30 define laterally and vertically offset portions 3l of the bearing segments. As seen most clearly in Fig, 8, the covering flange may closely overlie the covered flange to a variable extent, the upper and lower edges of the offset portions 31 being embraced between the extended ends of the hearing segments 17 and 18 and effectively blocking the escape of chips and other large particles through the variable gaps 32 between adjacent bearing segment ends.

The strainer plates are flat, rectangular plates which may be easily formed and drilled or otherwise perforated. The frame is easily cast as an integral construction. The strainer plates are easily laid in place, being supported on the intermediate ribs 2, and may be tack welded in position suiiiciently to hold the plates in place during usage, the welding permitting ready removal of the plates for replacement. The ribs are arched so that the circulating liquid may flow through the interiors of the various strainer sections to the suction pipe.

In Figs. 5, 6 and 7, a radial plane is indicated by the letter R. This plane is offset toward the covering fiange 29 quite a bit from the vertical centerline of the space between the side ribs 19 and 20, and all of the ribs lie parallel to this radial plane and are equally spaced from each other. Because of the offsetting of this plane, the inward projection of the rib 20 from the inner surface of the ydigester is less than the inward projection of the rib 19 from the inner surface of the digester. This, coupled with the elevation of the covering flange 29, and the central diminishing of both anges, particularly the covered flange 30, permits tight overlapping of the flanges to a variable extent. In both Pigs. 6 and 7 the anges are indicated as being slightly overlapped at the left sides of the figures and greatly overlapped at the right sides, indicating that the spacing of the frames is not critical and may vary accidentally or by design in order to have all frames overlap to define a complete screen annulus.

It has been empirically determined that a good width of frame to adapt the construction to all commercially encountered sizes of digesters is such that one frame would be employed for each four and three-quarter inches of the diameter of digester. Thus, in a digester having a nominal diameter of eight feet, as seen in Fig. 7, nineteen or twenty frames may be employed; while in a digester having a nominal diameter of eighteen feet, as seen in Fig. 6, forty-four to forty-six frames may be employed. The larger the number of frames utilized for each size of digester the closer the spacing between each pair of frames must be. It is recommended that the average spacing of frames be less than one inch, and if the average spacing becomes greater than one inch, another or two frames should be added, the number depending upon circumstances. For example, a nominal eight-foot digester may have a thin lining, in which case twenty frames may be utilized, but if a thick lining is utilized it may `be necessary to remove one frame, space each pair of frames to a greater extent, and thus reduce the number to nineteen.

As seen in Figs. 6 and 7, it will be appreciated that the radius of the outer surfaces of the bearing segments 17 and 18 is substantially midway between the maximum and minimum radii of the range of digester shells. Therefore, when employing the universally adaptable frame in a large digester, the ends, or one end, of each frame will be spaced from the shell lining, while in a small digester the centers of the frames will be spaced from the shell lining. This spacing is rather small and immaterial since the cracks thus form-ed will be covered and blocked by the preferred Z-strip supporting rings 14. Even if spaced supporting brackets are employed, it will generally be found that the cracks between the bearing segments and the surface of the lining will be too small to permit the harmless escape of all but the finest material.

It will be readily appreciated by those skilled in the art that the present design is readily suitable for fabrication of digester screens from stainless steels, thereby permitting the provision of long lasting, noncorrosive strainer screens. It is also to be appreciated that the present invention may be employed in digesters lined with stainless steel, or in unlined digesters, as distinguished from the brick-lined digesters herein illustrated and described. The screen sections may be directly welded to the metal wall of the digester in such cases, or the same supporting means as herein illustrated and described may be employed in order to facilitate replacement or cleaning.

Having illustrated and described my invention in what is considered to be the preferred embodiment thereof, it should be apparent to those skilled in the art that the invention permits of modification in arrangement and detail. I claim as my invention all such modifications as come within the true spirit and scope of the appended claims.

claim:

l. A sectional digester screen comprising a plurality of sections, each of said sections comprising a frame including an upper bearing segment, a lower bearing segment and a plurality of spaced ribs extending between said segments, and screening means covering the spaces between said ribs and segments, one side edge of each frame having a continuons covering ange extending laterally therefrom and closely overlying the inner surface of an adjoining frame throughout its length, said covering flange progressively decreasing in width from both ends toward its middle.

2. A sectional digester screen comprising a plurality of sections, each of said sections comprising a frame including an upper horizontal bearing segment, a lower horizontal bearing segment and a plurality of spaced ribs extending vertically between said segments, and screening means covering the spaces between said ribs and segments, one Vvertical edge of each frame having a continuous covering flange extending laterally therefrom and closely overlying the inner surface of an adjoining frame throughout its length, the ends of said covering ange merging into the inner surfaces of said bearing segments, and the opposite vertical edge of each frame having a continuous covered ange extending laterally therefrom and having its ends dening laterally and vertically offset portions of said bearing segments.

3. A sectional digester screen comprising a plurality of sections, each of said sections comprising an integral frame including an upper horizontal bearing segment, a lower horizontal bearing segment and a plurality of spaced ribs extending vertically between said segments and screening means covering the spaces between said ribs and segments, one vertical edge of each frame having a continuous covering flange extending laterally therefrom and closely overlying the inner surface of an adjoining frame throughout its length, the ends of said covering ange merging into the inner surfaces of said bearing segments, and the opposite vertical edge of each frame having a continuous covered flange extending laterally therefrom and having its ends defining laterally and vertically offset portions of said bearing segments,

the sum of the widths of said flanges decreasing from both ends toward the middle.

4. A sectional digester screen comprising a plurality of sections, each of said sections comprising a frame including an upper horizontal bearing segment, a lower horizontal bearing segment and a plurality of spaced ribs extending vertically between said segments, and screening means covering the spaces between said ribs and segments, one vertical edge of each frame having a continuous covering flange extending laterally therefrom and closely overlying the inner surface of an adjoining frame throughout its length, the ends of said covering ange merging into the inner surfaces of said bearing segments, and the opposite vertical edge of each frame having a continuous covered flange extending laterally therefrom and having its ends deiining laterally and vertically offset portions of said bearing segments, each of said flanges decreasing in width from its ends toward its middle.'

5. A sectional digester screen comprising a plurality of sections, each of said sections comprising a cast metal frame including an upper horizontal bearing segment, a lower horizontal bearing Segment and a plurality of spaced ribs extending vertically between said segments, and screening means covering the spaces between said ribs and segments, one vertical edge of each frame having a continuous covering ange extending laterally therefrom and closely overlying the inner surface of an adjoining ame throughout its length, the ends of said covering flange merging into the inner surfaces of said bearing segments, and the opposite vertical edge of each frame having a continuous covered flange extending laterally therefrom and having its ends dening laterally and vertically olset portions of said bearing segments, each of said ilanges decreasing in width from its ends toward its middle, said covered flange decreasing more than said covering ange.

6. A sectional digester screen comprising a plurality of sections, each of said sections comprising a frame incl'uding an upper horizontal bearing segment, a lower 4 horizontal bearing segment and a plurality 4of spaced ribs extending vertically between said segments, and screening means covering the spaces between said ribs and segments, one vertical edge of each frame having a continuous covering ange extending laterally therefrom and closely overlying the inner surface of an adjoining frame throughout its length, the outer surfaces of said bearing segments defining portions of a cylinder.

7. A sectional digester screen comprising a plurality of sections, each of said sections comprising a frame including an upper horizontal bearing segment, a lower horizontal bearing segment and a plurality of arched ribs extending vertically between said segments, and screening means covering the spaces between said ribs and segments, one vertical edge of each frame having a continuous covering flange extending laterally therefrom and closely overlying the inner surface of an adjoining frame throughout its length, the outer surfaces of said bearing segments dening portions of a cylinder, said ribs being equally spaced and each lying parallel to a radial plane offset toward said covering flange from the vertical centerline of the frame.

8. A sectional digester screen comprising a plurality of sections, each of said sections comprising a frame including an upper horizontal bearing segment, a lower horizontal bearing segment and a plurality of spaced ribs extending vertically between said segments, and screening means covering the spaces between said ribs and segments, one vertical edge of each frame having a continuous covering ange extending laterally therefrom and closely overlying the inner surface of an adjoining frame throughout its length, said ribscomprising a pair of side ribs and a pair of intermediate ribs, the inner surfaces of said side ribs lying inwardly from the inner surfaces of said intermediate ribs whereby a screen plate filling the space between said side ribs will be supported by said intermediate ribs and framed along its side edges by said side ribs.

References Cited in the le of this patent UNITED STATES PATENTS 312,672 Terry Feb. 24, 1885 826,193 Reinicke July 17, 1906 899,961 Edgerton Sept. 29, 1908 2,015,139 Dustan Sept. 24, 1935 2,062,127 Guettler et al. Nov. 24, 1936 2,340,925 Boyer Feb. 8, 1944 UNITED STATES PATENT OEEIOE CERTIFICATE OE CORRECTION Patent Non 2,852,369 September 16, 1958 Paul Eyolfson It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Gc1umn 6, list of references cited, under "UNITED STATES PATENTS, add the following;

Signed and sealed this 30th day of December 1958,.

- SEAL) Hest:

KARL Hf MINE ROBERT C. WATSON Attesting Ocer Commissioner Of Patents 

1. A SECTIONAL DIGESTER SCREEN COMPRISING A PLURALITY OF SECTIONS, EACH OF SAID SECTIONS COMPRISING A FRAME INCLUDING AN UPPER BEARING SEGMENT, A LOWER BEARING SEGMENT AND A PLURALITY OF SPACED RIBS EXTENDING BETWEEN SAID SEGMENTS, AND SCREENING MEANS COVERING THE SPACES BETWEEN SAID RIBS AND SEGMENTS, ONE SIDE EDGE OF EACH FRAME HAVING A CONTINUOUS COVERING FLANGE EXTENDING LATERALLY THEREFROM AND CLOSELY OVERLYING THE INNER SURFACE OF AN ADJOINING FRAME THROUGHOUT ITS LENGTH, SAID COVERING FLANGE PROGRESSIVELY DECREASING IN WIDTH FROM BOTH ENDS TOWARD ITS MIDDLE. 